Method of drilling wells



A B-ii 22, 1941. A. D. GARRISON METHOD OF DRILLING WELLS Filed Sept. 23, 1938 Amwzmokmv RPM ATTORNEYS Patented Apr. 22, 1941 UNITED STATES PATENT METHOD OF DRILLING WELLS Allen D. Garrison, Houston, Tex, assignor to The Texas Company, New York, N. Y., a corporation of Delaware Application September 23, 1938, Serial No. 231,282

11 Claims.

This invention relates to the drilling of wells and more particularly to the control of the heaving shale encountered in the drilling of such wells.

strength at the high temperatures encountered underground in the drilling of wells. According to my invention this is accomplished by the use of a mixture of aqueous sodium silicate, certain water soluble salts and suspended amorphous silica.

Drilling fluids are almost universally used in the drilling of wells employed for tapping underground collections of oil, gas, brines and water. These fluids fulfill various functions, the most important of which are to assist in the removal of cuttings from the wells, to seal formations of gas, oil and water which may be encountered at various levels and to lubricate the drilling tools and the drill pipes which carry the tools.

In the course of drilling wells, the bores may encounter certain geological formations which are termed heaving shale formations" or more simply "heaving shale. The term denotes shale strata which do not remain consolidated during the drilling operations. In some cases, the shale heaves or caves into the hole when the drilling tools are removed therefrom and in other cases the shale may heave in the course of the actual drilling. In the latter cases, the shale may bind "o'r pinch the drill stem, thereby preventing its rotation or even resulting in its destruction.

It appears that there are various types of heaving shales which react differently; some may be controlled merely by mechanical methods,

' whereas others require chemical treatment for successful control. advanced for explaining the heaving of shales Various theories have been whichhmay be controlled by mechanical means.

the drilling of a hole through the shale forms -1. an:opening. into which the shale can slide or J :mcave to partially relieve the inner stress.

The class of heaving shales which require chemical treatment for successful control apparently disintegrate when they are contacted with aqueous drilling fluids, and experiments indicate that it is the water content of the drilling fluids which brings about this disintegration. I jointly with William V. Vietti discovered, and have disclosed in and claimed in our co-pending Patent No. 2,165,823, dated July 11, 1939, that by incorporating relatively largequantities of certain sodium silicates in drilling fluids, it is possible by the use of such fluids to penetrate heaving shales successfully. We found that sodium silicates in which the ratio of silica to sodium oxide is greater than one, and preferably sodium silicates in which the ratio of silica to sodium oxide is greater than 1.5 to 1.0 may be employed, and, in fact, that sodium silicates up to and including sodium silicates having a ratio of silica to sodium oxide as high as 3.9 to 1.0 are successful. It is desirable to use not less than 20% by volume of the aforementioned sodium silicates in the preparation of drilling fluids.

The sodium-silicates which I propose to use in the practice of my invention are the commercially available sodium silicates, including both the readily soluble solid forms as well as the more common aqueous solutions. The latter are placed on the market in water solutions in concentrations near the practical limit of viscosity for the purpose of avoiding the expense of shipping unnecessary amounts of water. It is well known that these commercial aqueous sodium silicate solutions range in water content from about 35% for sodium silicates having a molecular ratio of 1.5:1, up to 70% for the sodium silicates having a molecular ratio of 3.9:1. In the practice of my invention I contemplate the use of commercial sodium silicates without regard to their method of preparation or their physical form.

William V. Vietti and I have also discovered and have disclosed and claimed in our co-pending Patent No. 2,165,824, dated July 11, 1939, that by incorporating certain types of water-soluble salts in combination with the sodium silicates indrilling fluids that substantial improvements may be obtained. These improvements consist principally of a. more complete protection of heaving shale and substantial reductions in the quantities of sodium silicate required in the drillingof heavingcshale wells.

The salts we discovered to be of value in combination with sodium silicates include one or more Thiocyanate Chlorate Iodide Nitrate Bromide Chromate I Chloride These salts are preferably used in an amount equal to at least 2% by weight of the aqueous medium of the drilling fluid. The quantities of salts may vary over wide limits and may be as high as the saturation value of a dissolved component of the aqueous medium.

I have observed that drilling fluids containing sodium silicate prepared in accordance with the foregoing inventions on encountering formations having unusually high temperatures, that is, temperatures in excess of 125 F., develop gel strengths which are in excess of'the range which is most satisfactory for drillingpurposes. The readjustments of the gel characteristics of the drillingfiuids necessary to counteract these undesirably high gel strengths involve expenditures which are avoided by my invention inasmuch as drilling fluids prepared in accordance with my invention have substantially the same gel strengths at widely different temperatures. For example, sodium silicate containing drilling fluids prepared in accordance with the aforementioned co-pending applications are suitable up 125 F. whereas drilling fluids prepared in accordance with my present invention are 'satisfactory not only at low temperatures but also at temperatures in excess of 125 F.

My invention may be applied by preparing an aqueous solution of sodium silicate or an aqueous solution of sodium silicate together with one capable of suspension in drilling fluids containing substantial amounts of sodium silicate.

As typical examples of the application of my invention I give herewith descriptions of several drilling fluids which have been found satisfactory for preventing the heaving of shales and which did not develop undesirably high gel strengths at elevated temperatures.

' The sodium silicate used in the examples had a molecular ratio of silica to sodium oxide of 2.0 to 1, and a water content of approximately 56.2%. The amorphous silica employed had a screen analysis as follows:

to approximately Per cent Passing 200' mesh 99 Passing 325 mesh 94 Smaller than microns 86.3 .Smaller than 25 microns 35.9 Smaller than 10 microns 12.0

Example I Per cent by weight Sodium silicate (34% by volume) 39.4 Sodium chloride 10.4: Amorphous silica 28.5 Water 1 21.4 Sucrose 0.3 The weight of this drilling fluid was 13.1 pounds per gallon.

Example II Per cent by weight *Sodium silicate (66% by volume) 46.5 Potassium chl i 10.4 Amorphous silica 32.5 Water.. 10.3 Sucrose 0.3

or more of the previously described water soluble salts and then suspending therein the required amount of amorphous silica or mixtures of the amorphous silica with barytes, iron oxide, litharge, or other weighting materials. The foregoing method of preparation is merely for the'purpose of illustration, and I do not intend to limit myself thereto.

I have also discovered that the addition of small quantities, usually in the neighborhood of from .2% to .8% by weight, of a sugar such as sucrose to the foregoing drilling fluids improves the physical character thereof insofar as the stability of the colloidal sodium silicate is improved as well as an increase in the wall building properties and a decrease in the rate of flow of fluid through the filter cakes formed on the walls of the hole by the drilling fluids. According to my experience this action of the sugar seems to be specific for sodium silicate drilling fluids of which the solid phase consists of suspended amorphous silica. Although I prefer sucrose as the stabilizing agent, other sugars, including dextrose, glucose, lactose, levulose and the like, may be successfully substituted therefor.

In the practice of my invention I propose to use at least 10% byweight of amorphous silica. It is to be understood however that the quantity employed may vary over wide limits above this value, being limited only by solids requirements of the particular drilling fluid. I do not intend to limit myself to the selection of any particular type of amorphous silica, and the only limitation to be imposed in the choice thereof is that it be of a sufficiently high degree of sub-division to be The weight of this drilling fluid was 14.1 pounds per gallon.

Example III Per cent by weight Sodium silicate (60% by volume) 50.0 Potassium chloride 11.2 Amorphous silica 27.5 Water 11.0 Sucrose; 0.3

The weight of this drilling fluid was 13.6 pounds per gallon.

The above drilling fluids readily lend themselves to use in the accepted manner and on being continuously circulated through the drill pipe to the locus of drilling pick up cuttings and drilling debris and carry them to the surface, where they readily drop the cuttings out in the settling pits. They prevent the heaving of shales with eminent success and display to a markeddegree the characteristic of not developing undesirable high gel strengths at high underground temperatures of 125 F. or above.

In order that those skilled in the art may more fully appreciate the significance of my invention, reference is had to Figure I wherein are shown a series of graphs depicting characteristics of drilling fluids prepared in accordance with my invention. In the same figure there are shown for comparison graphs of a sodium silicate containing drilling fluid which was not made up in accordance with my invention and which displayed the characteristic of developing high gel strengths at elevated temperatures.

Although there are several methods of determlning gel strengths, I have found that a good employing the e sees method ofdeterminihg the extent to which-a drilling fluid develops gel is provided by measuring the viscosity at several rates of shear. When the viscosity at low rates of shear is substantially higher than the viscosity at high rates of shear, high gel strength is indicated. For these determinations any viscosimeter capable of obtaining viscosities at different temperatures and at different rates of shear may be employed.

"In the case of the graphs shownon the aforementioned Figure I, a Stormer viscosimeter was employed and viscosity measurements were made respectively at 200, 400 and 600 revolutions per minute. The viscosities in centipoises so obtained were then plotted against the reciprocals of the speeds of the viscosimeter.

Referring to Figure I. and particularly the graplis shown thereon:

Graph A represents the curve obtained when g fluid shown in Example I at a temperature of86 F.

Graph B is the curve obtained with the same drilling fluid at a temperature 01' 145 F.

Graph represents the curve obtained with the drilling fluid shown in Example 11 maintained at a'temperature of 75 F.

Graph D is the curve of the same drilling fluid maintained at a temperature of 140 F.

From a study of these graphs it is quite apparent that inasmuch as the viscosity is not substantially'higher at low rates of shear than the viscosity at high rates of shear, the drilling fluids do not develop high gel strengths.

For purposes of comparison I have shown in the figure the curves obtained at low and high temperatures with a sodium silicate drilling mud containing clay, shale and barytes instead of amorphous silica. This drilling fluid was prepared by prepming an aqueous phase consisting of which was then weighted with clay, shale and barium sulphate to a weight of 13.3 pounds per gallon. Graph E represents the curve at 86 F.

I and Graph F represents the curve at 140 F.

The gel strength of this fluid at il6 F. is within the normal operating range, but if high temperatures were encountered during its use, its gel strength would exceed this normal operating range as is exemplified in Graph F.

Drilling fluids prepared in accordance with my invention readily lend themselves to the addition of weighting materials and. for this purpose I contemplate the use of barytes, litharge, inon oxide, or other suitable flnely divided solids.

Obvious many modifications and variations of the invention as hereinbeiore set forth may be made without departing from the spirit and scope thereof, and only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. A drilling fluid for drilling through heavi shale comprising sodium silicate in aqueous dispersion in an amount and of a character effective to prevent the heaving of shale, at least one salt selected from the group consisting of the sodiium and potassium thiocyanates, chlorates, iodides, nitrateabromides, chromates and chlorides, the salt content of the dispersion falling within the range of from 2% by weight or the aqueous medium up to the saturation value of the dissolved component, and suspended finelydivided amorphous silica in an amount sumcient to prevent the development of high gel strengths in the sodium silicate drilling fluid at temperatures above 125 F.

2. A drilling fluid for drilling through heaving shale comprising sodium silicate in an amount of notless than 20% by volume, in which the molecular ratio oisllica to sodium oxide falls within the range of from 3.9:1 to 1.5 1, at least one salt selected iroin the group consisting of the sodium and potassium thiocyanates, chlorates, iodides, nitrates, bromides, chromates and chlorides, the salt content of the dispersion falling within the range difrom 2% by weight of the aqueous medium up to the saturation value of the dissolved component, and suspended finely-divided amorphous silica in an amount suillcient to prevent the development of high gel strengths in the drilling fluid at temperatures above 125 F.

3. A drilllng fluid for drilling through heaving shale comprising sodium silicate in an amount of not less than 20% by volume, in which the molecular ratio of silica to sodium oxide falls within the range of from 3.9:1 to 1.521, at least one salt selected from the group consisting of the sodium and potassium thiocyanates, ch1orates, iodides, nitrates, bromides, chromates and chlorides, the salt content of the dispersion falling within the range of from 2% by weight of the aqueous medium up to the saturation value of the dissolved component, and suspended finely divided amorphous silica in an amount of at least 10% by weight of the drilling fluid.

4. In the drilling of wells with the use of a drilling fluid, the method of preventing the heaving of shale encountered in the well which comprises circulating through the well a drilling fluid comprising sodium silicate in aqueous dispersion in an amount and of a character efifective to prevent the heaving of shale, at least one salt selected from the group consisting of the sodium and potassium thiocyanates, chloratcs, iodides, nitrates, bromides, chromates and chlorides, the salt content of the dispersion falling within the range of from 2% by weight of the aqueous medium up to the saturation value of the dissolved component, and suspended finely-divided amorphous silica in an amount suflicient to prevent the developementof high gel strengths in the sodium silicate drilling fluid at temperatures above F.

5. In the drilling of wells with the use of a dnilling fluid, the method of preventing the heaving of shale encountered in the well which comprises circulating through the well a drilling fluid comprising sodium silicate in an amount of not less than 20% .by volume, in which the molecular ratio of silica to sodium oxide falls within the range of from 3.9:1 to 1.5:1, at least one salt selected from the group. consisting of the sodium and potassium thiocyanates, chlorates, iodides, nitrates, bromides, chromates and chlorides, the salt content of the dispersion falling within the range of from 2% by weight of the aqueous medium up to the saturation value of the dissolved component, and suspended finely divided amorphous silica in an amount of at least 10% by weight of the drilling fluid.

6. A drilling fluid for drilling through heaving shale comprising 39.4% by weight of sodium sillcate having a molecular ratio of silica to sodium oxide of 2:1, 10.4% by weight of sodium chloride.

silica, 0.3% by 28.5% by weight of amorphous weight of sucrose, and 21.4% by weisht of we.

,7. A drilling fluid for drilling through heaving' shale comprising 46.5% by weight of sodium silicate having a molecular ratio of silica to 80- -dium oxideor 2: 1, 10.4% by weight oi potassium chloride, 32.5% by'weight oi amorphous silica, 0.3% by weight of sucrose, and 10.3% by weight of 8. A drilling fluid-for drilling through heaving shale comprising 50.0% by weight of sodium silicate having a-molecular ratio of silica to sodium oxide oi 2:1, 11.2% by"weight' of potasslum chloride, 27.5% by; weight of itinnillilons silica, 0.3% by weight of sucrose, and 11.0% by drilling through heaving'shale comprising sodium silicate in an amount o Lnot less than 20% by volume eii'ective to preweight of water.

.9.-A drilling fluid for venvthewlreaving o! shale, the sodium silicate a molecular irat'io ot 'silica to sodium '-j the range of 3.9:1-to 1.53, ms-

amorphous silica in an S6 'weight ortheiirilling 10. In the drilling ,or wells with the use of a drilling fluid, the method of preventing the heaving of shale encountered inthe well which comprises circulating through the well a drilling fluid comprising sodium silicate in an amount of not less than 20% by volum'e'efiective to prevent the heaving of shale, the sodium silicate having a molecul-arratio of silica to sodium oxide within the range of 3.9:1 to 15:1, and suspended finely-divided amorphous silica in an amount of at least 10% by weight oi the drilling fluid sufllcient to prevent the development of high; gel strengths in the silicate drilling fluid at temperatures above 125. .F'. a

11. In the drilling of wells with the use of -9.

drilling fluid, the method of preventing the heaving of shale encountered in the well. which comprises circulating through the well a'drillingfluid.

comprising-sodium silicate in an amount ancLof shale. and suspended silica 'in an amount sumcientltoprevent the de a character eflective to prevent the heaving of finely-divided amorphous velopment of high gel strengths, in the sodium drilling: fluid at temperatures above n fiansiison'. 

